Language, the code of verbal communication, requires agreement among its users on signals and patterns of signals to be used in the exchange of information about perceptions of persons, objects, and events. Such agreement is important in the development of the conceptual framework within which the individual learns to organize his perceptions; for it specifies features that must be represented by signals in all exchanges of information with other members of the same social group. Features specified in this way must be specially observed. The exchange of information is used by the individual in making decisions about behavior in a given socio-cultural setting. Linguistic analysis leading to accurate descriptions of language systems may be useful, therefore, in the definition of conceptual systems and in the determination of ways in which individuals organize their perceptions of conditions, events, and socio-cultural settings. Analysis of the language of addicts can be useful in determining significant features of conditions and events that members of this group have learned to include in exchanges of information. Accurate description of the addict's language may furnish useful data about the conceptual framework of the addict and his perceptions of the socio-cultural environment in which he functions. This proposal is the description of a research program designed to analyze the language of a sample group of addicts and to produce a structural description of that language. The structural description may then be used as the basis for statements about the conceptual systems of addicts and for statements about socio-cultural environments as perceived by the addict. The results will be useful in developing programs of therapy, rehabilitation, and education for the prevention of drug abuse; for structural features of the language of addicts are important in determining how information intended for addicts and potential addicts must be structured to guarantee its reception. Furthermore, information about the conceptual system of addicts may be used in future comparative studies to determine differences between the systems of addicts and non-addicts.